Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0042—Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
  • G01L9/0008—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations
  • G01L9/0019—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a semiconductive element
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
  • G01L9/0073—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a semiconductive diaphragm
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/0802—Details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
  • G01P2015/0822—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass
  • G01P2015/0825—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass for one single degree of freedom of movement of the mass
  • G01P2015/0828—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass for one single degree of freedom of movement of the mass the mass being of the paddle type being suspended at one of its longitudinal ends

Definitions

• the present invention relates to the field of capacitive silicon micro-sensors.
• Such micro-sensors can for example constitute pressure sensors, acceleration sensors, etc.
• micro-sensors In recent years, new types of silicon micro-sensors have been developed, taking advantage of the silicon etching techniques developed in the context of the manufacture of semiconductor electronic components.
• such micro-sensors consisted of an assembly of suitably engraved silicon wafers and thin glass slides serving as a sealed housing or insulating separation plates between silicon wafers, these glass slides possibly bearing various patterns. of metal electrodes.
• the sensor of Figure 1 is an acceleration sensor and the sensor of Figure 2 a pressure sensor.
• Each of these sensors includes a central silicon wafer 1 sandwiched between external silicon wafers 2 and 3.
• the insulation between the wafers is provided by a first insulating strip, generally a layer of silicon oxide, between the pads 1 and 2 and a second insulating strip 6 between the pads 1 and 3.
• These insulating strips take the form of a frame disposed between adjacent pads, along the edges thereof. Oxide layers can be obtained by growth or deposition from one of the adjacent platelets.
• the facing silicon and silicon oxide surfaces have very low roughness, for example less than 0.5 nm.
• the extreme silicon wafers 2 and 3 define between them and with the frame part of the silicon wafer 1 a region in which a controlled atmosphere is contained.
• FIG. 1 schematically represents a sectional view of an accelerometer
• the central silicon wafer 1 is etched before assembly to include a frame and a central plate or counterweight 8 fixed to the frame by thin bars of suspension 9.
• a single bar appears in the schematic sectional view of FIG. 1.
• suspension systems with one to four bars will be used.
• the external plates 1 and 3 define with the frame formed at the periphery of the central plate an empty space. Capacity variations are detected between the upper face of the counterweight and the silicon wafer 3 and possibly also between the lower face of the counterweight and the lower wafer 2.
• the counterweight 8 moves by compared to the whole device and the aforementioned capacities vary.
• An electrostatic servo is also generally provided to hold the counterweight in place by applying a continuous electric field and it is then the error signal which gives an indication of the variation in capacity.
• FIG. 2 very schematically represents a structure constituting a pressure sensor.
• the lower plate 2 is etched to form a thin membrane there.
• the plate 1 is etched to form a stud 12 supported on this membrane.
• a silicon strip 13 extends between this pad and the frame of the wafer 1.
• Variations in external pressure deform the membrane 11 and cause a deformation of the tension of the lamella 13.
• This variation in tension causes a variation in the resonant frequency of the resonator formed by the lamella 13.
• the variation in frequency is deduced from the variation capacity between the strip 13 and the facing surface of the wafer 3.
• the internal face of the wafer 3 is etched to form a projecting strip opposite the strip 13.
• electrodes 21, 22 and 23 must be respectively integral with the plates 1, 2 and 3. In the case of FIG. 2, only the electrodes 21 and 23 will be necessary.
• the object of the present invention is to provide a particular structure at the level of the insulating layer, so as to reduce the surface of the parasitic capacitors at the level of the frame formed in the wafer 1 and the opposite parts of the upper and / or lower plate.
• the subject of the invention is a capacitive micro-sensor comprising a sandwich of three silicon wafers 1, 2, 3, a peripheral strip of each face of the central wafer being attached to a corresponding strip of the opposite face d '' an external plate by means of an insulating strip 5, 6, at least one of the external plates constituting a first electrode, the central plate constituting a second electrode 21 and at least a part of this central plate forming a capacity variable with at least one of the external plates, characterized in that at least one insulating strip has a honeycomb surface so as to reduce the contact surface between said strip and the facing silicon wafer.
• the peripheral strip or strips of the central plate can advantageously include engravings at the level of the cells of the insulating strip.
• peripheral strips of the external plates can also have engravings opposite the cells of the insulating strip.
• the capacitive micro-sensor constitutes an accelerometer
• the above-mentioned part of the central plate forms a suspended weight
• the lower plate comprises a thinned part forming a membrane and the central plate comprises a stud mounted on this membrane and a strip extending between the stud and a peripheral part. of this central plate, this strip forming with the upper plate a capacitive resonator of variable characteristics as a function of the pressure applied.
• the insulating strip attached to a corresponding strip on the opposite face of an external plate, which protrudes from said corresponding strip, thus ensuring better electrical insulation.
• the first and second insulating layers are made of silicon oxide.
• the present invention also provides a method of manufacturing a micro-sensor which consists in etching the central plate to form a frame and a sensitive central part, the two faces of the frame being coated with a layer of silicon oxide, said oxide layer being etched so as to give it a cellular structure; forming on one side, facing the central plate, of each of the external plates a frame made of locally etched silicon; and assembling the external plates and the central plate, the cells of the oxide layer being opposite the engravings produced in the external plates.
• FIG. 1 illustrates a schematic sectional view of an acceleration microsensor according to the prior art
• FIG. 2 illustrates a schematic sectional view of a pressure microsensor according to the prior art
• FIG. 3 illustrates a schematic sectional view of an acceleration microsensor according to the invention
• FIGS. 4a, 4b and 4c illustrate the steps of a manufacturing method according to the invention making it possible to obtain a micro-sensor with cellular oxide with a protruding insulating strip.
• the relative thicknesses of the various layers and the relative dimensions of the various elements are not to scale but have been arbitrarily drawn to facilitate the readability of the figures.
• the lateral faces of the various silicon wafers have been shown as etched obliquely, in accordance with the appearance which these lateral faces take when a conventional anisotropic etching of silicon has been carried out according to the plans (1 1 1). Conventionally, this is a chemical etching which can be carried out in a KOH solution.
• Figure 3 is a schematic sectional view of an acceleration microsensor in which the parasitic capacitances have been reduced, by playing on the surface of the parasitic capacitors.
• the assembly of the three silicon wafers is generally carried out by high temperature welding (900 to 1100 ° C); after cooling, significant stresses are exerted between the oxide layers and those of silicon, the thermal expansion coefficients of which are different. By reducing the contact surface between these layers of different nature, the aforementioned constraints are minimized.
• the silicon oxide is etched for example by HF solution to obtain the honeycomb structure.
• the external silicon wafers are also etched so as to further reduce the parasitic capacities inherent in the device.
• the width of the etched patterns can be of the order of ten micrometers, such as the size of the cells produced at the silicon oxide layers.
• the size of the external plates is smaller than that of the central plate so as to achieve better electrical insulation, due to the overflowing oxide as illustrated in FIG. 4.
• the manufacture of a micro-sensor results from a collective process, each wafer initially forming part of a larger silicon wafer, the separation into micro- individual sensors being made after the final assembly operations and possibly contact formation.
• this separation is carried out by sawing and, during sawing, particles of silicon can be entrained towards the touching zones which can cause short circuits at the level of the silicon wafers, due to the thin thickness of the layers.
• silicon oxide approximately 1 ⁇ m
• Figure 4 illustrates the assembly of three silicon wafers during a soldering step.
• the dotted lines are representative of the cutting of the individual micro-sensors.
• the outer pads are defined by the same type of KOH engraving as the central pad.
• the oxide surface projecting at the level of the central plate can typically be of the order of 100 micrometers and thus contribute to ensuring better electrical insulation.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Pressure Sensors (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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ID=9481612

Family Applications (1)

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Cited By (2)

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Citations (2)

• 1995
  • 1995-08-01 FR FR9509366A patent/FR2737610B1/fr not_active Expired - Fee Related
• 1996
  • 1996-07-19 DE DE69616260T patent/DE69616260T2/de not_active Expired - Fee Related
  • 1996-07-19 EP EP96926435A patent/EP0783676B1/de not_active Expired - Lifetime
  • 1996-07-19 WO PCT/FR1996/001143 patent/WO1997005463A1/fr active IP Right Grant

Patent Citations (2)

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